# The Naked Scientists Forum

### Author Topic: Potential 'energy', but, on a ledge? Will it add mass?  (Read 7044 times)

#### MikeS

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##### Re: Potential 'energy', but, on a ledge? Will it add mass?
« Reply #25 on: 20/03/2012 06:44:20 »
Matt
As per your request I have moved it to new theories.
However, I still think it is almost wholly GR with just an extra dot or two connected.

#### JP

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##### Re: Potential 'energy', but, on a ledge? Will it add mass?
« Reply #26 on: 20/03/2012 13:26:37 »
Connecting extra dots that are above and beyond the original theory generally makes it a new theory.

Going back to Yor_on's original question, whenever you think of a whole system, putting energy in increases its inertial mass.  If I have a box consisting of mirrored sides and I inject photons, the inertial mass of the box appears to go up.  By the equivalence principle, its gravitational mass should also go up.

This is evident in mass all around us, which is primarily caused by binding energies in the nucleus.

As is often the case when you try to use simple ideas like mass in general relativity, a full accounting of how this all happens dynamically as you raise the mass will probably require using the stress-energy tensor, rather than just energy/mass.
« Last Edit: 20/03/2012 13:31:47 by JP »

#### Pmb

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##### Re: Potential 'energy', but, on a ledge? Will it add mass?
« Reply #27 on: 20/03/2012 13:57:21 »
The 'potential' stuff is just that, 'potential'. And it's the relation and final interaction that will define the outcome. So you could say that this 'potential energy' is 'spread out' in space, potentially there, but only as a result of and in a interaction.
...
The spring though has been compressed, which is an interaction, and a outcome. There's nothing 'potential' about that compressed spring.
Sure there is. A compressed spring has an associated potential energy to it.
Which one is correct? My self I see 'potential energy'  as a relation basically, only satisfied in its final outcome. Against it we have the idea that elevating something in a gravitational field will add a rest mass to the object, in this case a ball resting on a ledge?
Einstein shows in his Meaning of Relativity text that, for a particle at rest, the  proper mass m (magnitude of 4-momentum, has a different mass as the rest mass (relativistic mass when at rest). When Einstein says in that text that he has demonstrated GR satisfying Mach's Principle, that is precisely what he meant.

#### yor_on

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##### Re: Potential 'energy', but, on a ledge? Will it add mass?
« Reply #28 on: 04/04/2012 01:47:52 »
Pete, as you compressed that spring, the energy is not 'potential' any longer as I see it. To me it has to be stored 'locally' inside the locked spring. And that's what I mean, I don't care for how long that spring is locked, but as long as it is and the material still keeps its original properties there will be a added 'real mass' to it, as I think of it, not 'potential'. But it is weird :)

How and what stores it inside that spring?

The way the atoms gets disturbed will dissipate with time and they will find their new equilibrium. So where should I place that 'energy'?
=

It must be the result of a changed geometry at least, as I think of it?
« Last Edit: 04/04/2012 02:45:58 by yor_on »

#### yor_on

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##### Re: Potential 'energy', but, on a ledge? Will it add mass?
« Reply #29 on: 04/04/2012 02:49:19 »
Let's assume a rubber band that you stretch. As we do, do the atoms move away from each other, they should, shouldn't they? Will the rubber band have an added mass if kept stretched. And how would that too be a result of a changed geometry locally?

If compared to compressing a spring?

#### The Naked Scientists Forum

##### Re: Potential 'energy', but, on a ledge? Will it add mass?
« Reply #29 on: 04/04/2012 02:49:19 »